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GPS Communication Software GPS Mapping Program Tarpits and Tips Tarpits and Tips Tools of the Trade Tools of the Trade - Part IV Tarpits and Tips TIPS Outline Datums Error, Accuracy, and Precision Map Scale and Errors Tips for Managing GPS Error Better Maps for GPS GPS Datum Tarpit

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Presentation Transcript
tools of the trade

GPS CommunicationSoftware

GPS

Mapping Program

Tarpits and Tips

Tarpits and Tips

Tools of the Trade
tools of the trade part iv
Tools of the Trade - Part IV

Tarpits and Tips

TIPS

outline
Outline
  • Datums
  • Error, Accuracy, and Precision
  • Map Scale and Errors
  • Tips for Managing GPS Error
  • Better Maps for GPS
gps datum tarpit
GPS Datum Tarpit
  • What’s the big deal
    • A football field of difference if you are wrong!
    • Ask the 3 soldiers in Afghanistan
gps datum tarpit6
GPS Datum Tarpit
  • Summary:
    • Know your Datum at all times
    • When you hear WGS84, it’s the same as NAD83

Aviation GPS is always WGS84

error accuracy and precision
Error, Accuracy, and Precision
  • Importance
    • Safety
    • Make or break a GIS project
  • Learn ways to keep GPS errors to a minimum
  • Be aware of the issues

Kenneth E. Foote and Donald J. Huebner, The Geographer's Craft Project, Department of Geography, The University of Colorado at Boulder.

basic definitions
Basic Definitions

1.) Accuracy: how close to truth or accepted values.

2) Precision: how repeatable or consistent

basic definitions9
Basic Definitions

3.) Error: includes both the imprecision of data and its inaccuracies

Accurate + Precise

= Low Error !

false advertising
False Advertising
  • Beware of False Accuracy and False Precision
    • UTM = 1 meter
    • DMS.S = Translates to about 3 meters
map scale
Map Scale
  • Accuracy and Precision for a map are a function of the scale at which the map was created
  • Applies for digital or paper
  • National Mapping Accuracy Standards employed by USGS
accuracy standards for various map scales
Accuracy Standards for Various Map Scales
  • 1:2,400 ± 6.67 feet
  • 1:24,000 ± 40.00 feet
  • 1:63,360 ± 105.60 feet
  • 1:100,000 ± 166.67 feet
map scale13

1:2,400

R=6.67’

1:12,000

R=33.33’

1:24,000

R=40’

Map Scale
map scale and the garmin
Map Scale and the Garmin
  • Question? Will your Garmin III Plus meet Mapping Accuracy standards for a 1:24,000 scale product?
  • How about a 1:63,360?
  • Today, we will answer that question?
sources of map errors
Sources of Map Errors
  • Age of Data
  • Map Scale

Mapsource data is 1:100,000 scale

  • Digitizing Errors
tips for managing gps error
Tips for Managing GPS Error
  • Record Metadata:
    • Who, What, Why
managing gps error
Managing GPS Error
  • Try to average points
managing gps error20
Managing GPS Error
  • Try to use Antenna when possible
make better maps for gps
Make Better Maps for GPS
  • Basic Premise:
    • Maps and GPS are made for each other
    • Location finding requires map grids, labeled tics and graticules
  • Ingredients Required:
    • ArcView
    • Coordinate Grid Maker extension*
    • Map Data

*Christoph Feldkotter Version 2.270 Available from www.esri.com/arcscripts

summary
Summary
  • Importance of Datums
  • How error free are you?
  • By managing error you can beat the odds